In laminated ceramic capacitors, for the purpose of reduction in size (reduction in thickness), it is effective to attempt to reduce in thickness not only of dielectric ceramic layers, but also of internal electrodes. However, when the internal electrodes are further reduced in thickness, electrode disconnection is likely to be caused as a result of a firing step for sintering of a raw laminated body. For example, the following technique has been proposed as a technique which can prevent the electrode disconnection.
In Japanese Patent Laid-Open Publication No. 2008-226941 (Patent Document 1), the rate of temperature rise adjusted to 500° C./hour to 5000° C./hour in a firing step prevents electrode disconnection to achieve an electrode thickness of 0.8 to 1 μm.
In Japanese Patent Laid-Open Publication No. 2000-216042 (Patent Document 2), structural defects such as cracks are prevented to increase the reliability of a laminated ceramic capacitor obtained, in such a way that the rate of temperature rise is adjusted to 500° C./hour or more at 700° C. to 1100° C. in a temperature rising process for firing, the oxygen partial pressure in the atmosphere is adjusted to 10−8 atm or less at 1100° C. or more, and the oxygen partial pressure is adjusted to 10−8 atm or more partially at 1100° C. or less in a temperature falling process.
In Korean Patent Laid-Open Publication No. 10-2006-0135249 (Patent Document 3), the temperature is increased at a rate of temperature rise of 10° C./second up to a temperature 20° C. lower than the maximum temperature to achieve a balance between the prevention of electrode disconnection and the prevention of overshoot during the temperature rise (reaching a temperature higher than a desired firing temperature during the temperature rise).
While the prior art described in any of Patent Documents 1 to 3 achieves the effect of allowing the internal electrodes to be reduced in layer thickness by means such as increasing the rate of temperature rise, the effect has a limitation, and for example, in a laminated ceramic capacitor including internal electrodes containing Ni as a conductive component, it is extremely difficult to achieve 0.3 μm or less as an electrode thickness after firing.
In addition, the atmosphere for firing a raw laminated body including internal electrodes using a base metal as a conductive component is, for example, a N2/H2/H2O system which needs to be controlled on a more reducing side than a Ni/NiO equilibrium oxygen partial pressure, and this need will restrict the equipment and the material design.
In addition, when the ceramic contains, for example, a volatile component such as Li, this volatile component is likely to scatter during firing. Further, the residual volume of the volatile component is likely to vary depending on the size of the raw laminated body to be fired, that is, the chip size, and the amount of charging a firing furnace, and it is difficult to suppress the variation in this residual volume.
On the other hand, a ceramic containing a BaTiO3 system as its main constituent has been typically used as a dielectric ceramic constituting dielectric ceramic layers included in laminated ceramic capacitors. Further, the ceramic containing the BaTiO3 system as its main constituent preferably contains a rare-earth element Re (Re is at least one selected from Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) as an accessory constituent, mainly for the improvement of reliability.
However, the Re fails to improve the reliability sufficiently, unless the Re is present as a solid solution moderately in the main constituent grains. It is to be noted in this case that the Re that is present as a solid solution does not always have to be present as a solid solution in the entire main constituent grains, and for example, may be present as a solid solution to such an extent that a core-shell structure is formed.
Therefore, when a lot of thermal energy is applied in order to make the Re present moderately as a solid solution, the solid solubility of the Re is improved, while the segregation of the Re is also increased, thereby leading to a decrease in reliability in the case of a thin layer of a laminated ceramic capacitor.
In addition, when the content of Re is increased significantly, there is a possibility that the dielectric constant of the dielectric ceramic will be decreased.    Patent Document 1: Japanese Patent Laid-Open Publication No. 2008-226941    Patent Document 2: Japanese Patent Laid-Open Publication No. 2000-216042    Patent Document 3: Korean Patent Laid-Open Publication No. 10-2006-0135249